The present invention relates to a semiconductor device for motor driving and a motor having the semiconductor device, a motor driving apparatus and an air conditioner.
Inverter-controlled three-phase brushless motors are widely adopted recently as motors of electrical household appliances and industrial machines. Price competition is severe particularly for electrical household appliances. It is desired to supply inexpensive inverters. A 120-degree rectangular wave driving method is therefore adopted as an inverter operation method, because this driving method uses a relatively simple circuit structure, can increase a motor efficiency and provide an inexpensive inverter.
With reference to FIG. 12, description will be made on an example of a 120-degree rectangular wave driving method according to prior art. In FIG. 12, reference numeral 1 represents a commercial power source and reference numeral 2 represents a power source circuit. VDC, Vcc and Vm are generated from AC voltage of the commercial power source 1. VDC is a main power supply voltage for inverter motor drive, Vcc is a power supply voltage for driving circuits in a semiconductor device 100 which drives a 120-degree rectangular wave driving type motor, and Vm is a power supply voltage for a microcomputer 3. The microcomputer 3 outputs a speed command signal Vsp to a motor 50 and receives a speed signal FG from the motor 50. The power source circuit 2 and microcomputer 3 are mounted on a first board 4.
The motor 50 has a board 60 built in the motor. The semiconductor device 100 for driving the 120-degree rectangular wave driving type motor, a Hall IC 90 and a shunt resistor Rs are disposed on the board 60 built in the motor. Coils 8 are connected to output terminals of the semiconductor device 100 for driving the 120-degree rectangular wave driving type motor.
FIG. 13 is a timing chart illustrating the 120-degree rectangular wave driving method. A to C in FIG. 13 indicate magnetic pole position signals VHU′, VHV′ and VHW′, and D to F in FIG. 13 indicate the outline of waveforms of output voltages VUM′, VVM′ and VWM′. The semiconductor device 100 for driving the 120-degree rectangular wave driving type motor outputs an H signal and an L signal each having a 120-degree electrical angle period, in accordance with the magnetic pole position signals VHU′, VHV′ and VHW′. Current flows through the coils 8 during the 120-degree period, and a non-feeding period of 60 degrees exist between respective 120-degree periods. As the motor is driven by the 120-degree rectangular wave driving method, torque ripples of the motor become large so that noises are likely to be generated during motor driving.
As a method of reducing noises of a motor, JP-A-2004-120841 (Patent Document 1) discloses a method of changing a phase current to a quasi sine waveform with low cost by using analog circuits.
Another method of reducing noises of a motor is a method called a sine wave driving method which changes a phase current of the motor to a sine waveform. High performance and low price of a microcomputer is advancing nowadays, and the sine wave driving method using a microcomputer is an optimum method of reducing noises of a motor.
Reference may be made to descriptions from paragraph (0020) to paragraph (0025) and from paragraph (0046) to paragraph (0049) of JP-A-2004-120841 (Patent Document 1).